I run both a Perma-cool eletric and a "Taurus" fan on 2 of my trucks. I would recomend the Taurus just because you can get them for cheap and they are great, I run the AC on the low speed and use the high speed on a temp sender. just make sure you use a big enough rated relay for the high speed as it takes some juice to run.
Painless wireing sells a great wire harness w/ sender for this, I used the relay it came with to run the low speed(hooked tothe AC clutch) and a larger relay for the high speed(hooked to the temp sender).